Technical Field
The present invention relates to a joint driving device a robot.
Related Art
In a vertical multi-joint type robot, in which a plurality of links are connected by turning joints, and a scalar type robot, the following plurality of lines have to be provided between a base and a tip of an arm: a power line and a signal line for driving a motor; a signal line for driving equipment, such as a hand, that is operated by a user; an air tube; and a high speed communication line for using a camera that detects an object.
PCT publication No. 2004-078423 discloses that a turning center of a turning joint has a vacant space (hole). Because wiring lines and tubes pass through the vacant space (hole) turning center, a motor, reduction gears and a shaft bearing are formed in a single integral unit.
JP publication No. 2010-284777 discloses a method that reduces a risk of breaking of wire and friction wear because a load to wiring lines and tubes decreases by absorbing a rotary motion of a joint by a U-shaped bent structure. Specifically, a plurality of cables, which is in a flat shape with a U-shaped bent state, are located in a turning side cable guide that is folded a turning shaft of a servomotor back to a motor side.
However, in the PCT publication No. 2004-078423, when the hole through which the wiring lines and tubes pass is provided at a center of an input-output shaft of the reduction gears and the motor shaft, a size of the joint in a radial direction increases so that an arm is thicken and an arm weight increases. Further, when the hole through which the wiring lines and tubes pass is provided at the center of the input-output shaft of the reduction gears and the motor shaft, an outer diameter of the motor shaft rotating in high speed and an outer diameter of the input-output shaft of the reduction gears increase. As a result, because circumferential speed of those shafts increases, grease and a lubricant for a motor shaft bearing and the reduction gears are spilled and friction heat from a contact area between a grease seal lip part and a high speed rotation shaft increases. That problem limits joint operation speed. Further, acceleration of the joint is limited because a torque generated by the motor is consumed by increased frictional resistance. Further, when the hole through which the wiring lines and tubes pass is provided at the center of the input-output shaft of the reduction gears and the motor shaft, the acceleration of the joint is limited because a motor torque is consumed at the time of acceleration and deceleration because inertia on a side of the input-output shaft of the reduction gears. Because the above problems become more serious for a joint driving device with a smaller shaft diameter and a small capacity, the above vacant space (hole) wiring structure is not appropriate to a joint mechanism of a small robot.
In JP publication No. 2010-284777, a motor cover is provided at an outer circumference of the servomotor. Because the cable guide is located at the outer circumference, a space is required between the motor and the motor cover. As a result, an outer diameter of the joint increases. Further, because the cable, which is in a flat shape, is located along with the cable guide in a shaft direction, another space for arranging the cable in the shaft direction. As a result, a width of the joint increases. According to the above described reasons, this method is applied to a limited area, such as a base of a robot arm, because the space is required for storing the wiring lines and tubes.